hostname — Local host name configuration file
/etc/hostname
The /etc/hostname file
                configures the name of the local system that is set
                during boot, with the
                sethostname(2)
                system call. It should contain a single
                newline-terminated host name string. The
                host name may be a free-form string up to 64 characters
                in length, however it is recommended that it consists
                only of 7bit ASCII lower-case characters and no spaces or dots,
                and limits itself to the format allowed for DNS domain
                name labels, even though this is not a
                strict requirement.
Depending on the operating system other configuration files might be checked for configuration of the host name as well, however only as fallback.